I propose that when answers or attempted answers are posted, we use the white font color. The text is difficult to read normally and if someone wants to read it, they can highlight the text. Most web browsers will highlight the text in such a way that it is readable when you select the white colored text.

Example: This is a sentence in white.

This way, anyone who wishes to still work out a puzzle, won't have their eye accidentally absorb information that might ruin the puzzle.